qcom: cpu_ops: power collapse the secondary cpus during hotplug.

During hotplug, call msm_pm_hotplug_enter to put the secondary cpus
into power collapse instead of just executing wfi instruction.

Change-Id: I26e0c856b00366a749bd09c751bf42a736d19013
Signed-off-by: Anji Jonnala <anjir@codeaurora.org>